As a conventional multiphoton-excited measuring device, there is known a multiphoton-excited microscope system such as one shown in FIG. 6, for example (see Patent Document 1, for example). In the multiphoton-excited microscope system, a short pulse laser light source 101 having a titanium-sapphire laser emits an optical pulse I with a pulse width of about 100 fs and a spatial distribution being of nearly perfect circle, and the optical pulse I transmits through free space to be incident on a pre-chirping unit 102.
The pre-chirping unit 102 has four diffraction gratings 121, 122, 123 and 124, and the incident optical pulse I is first diffracted and reflected, with respect to each of wavelength components thereof, in a different angular direction in the plane of the paper in FIG. 6 by the diffraction grating 121. It is noted that the angular direction to which wavelength components of the optical pulse I are reflected by the diffraction grating 121 in the vertical direction of the plane of the paper in FIG. 6, is constant. Next, the optical pulse I is diffracted and reflected by the diffraction grating 122 with respect to each of wavelength components in the same way. The spatial distribution of the optical pulse I after diffracted by the diffraction grating 122 is elliptical with a vertical direction of the plane of the paper in FIG. 6 as a long axis when seen from a transmitted direction of the optical pulse I. Thereafter, the optical pulse I is sequentially diffracted and reflected by the diffraction gratings 123, 124 in the same way as by the diffraction gratings 121, 122, and emitted from the pre-chirping unit 102 after its spatial distribution becomes of nearly perfect circle again.
As above, the optical pulse I is sequentially diffracted by four diffraction gratings 121, 122, 123, 124 in the pre-chirping unit 102, thereby the temporal width of the optical pulse I is expanded, before or after the pre-chirping unit 102, to temporally ahead for its short wavelength components and behind for its long wavelength components due to the difference of transmission distance depending on wavelength components. Such a state of optical pulse is generally referred to as a chirp pulse. In FIG. 6, the schematic time waveform of the optical pulse I is also represented with a horizontal axis as time and a vertical axis as a light intensity.
The optical pulse I emitted from the pre-chirping unit 102 transmits through free space and passes through a coupling device 103 to be incident on a single-mode optical fiber 104. The single-mode optical fiber 104 has a difference in a transmission speed for a wavelength which is called wavelength dispersion, and a zero-dispersion wavelength determined based on materials or the like distinguishes between a normal dispersion region and an anomalous dispersion region. In the normal dispersion region, the transmission speed of light is higher with a long wavelength than with a short wavelength, and the opposite is in the anomalous dispersion region. Here, the single-mode optical fiber 104 normally-diffuses the optical pulse I. Therefore, the optical pulse I in which short wavelength components are temporally ahead transmits through the single-mode optical fiber 104, and then long wavelength components which have been temporally behind catch up with short wavelength components which have been temporally ahead, resulting in the formation of a time waveform similar to one at the time the optical pulse I is oscillated from the short pulse laser light source 101.
The optical pulse I having transmitted through the single-mode optical fiber 104 is incident on a microscope 105. With respect to the optical pulse I incident on the microscope 105, a coupling optical system 151 expands its spatial distribution to render the pulse to be parallel light. It is noted that a pinhole 152 is disposed at a light focus point of the optical pulse I in the coupling optical system 151 to remove light noises of the optical pulse I. Subsequently, the optical pulse I is reflected by a dichroic mirror 153 and collected on a sample 156 by an image-forming optical system 155. It is noted that a scan unit 154 scans the light focus point of the optical pulse I on the sample 156 in a plane perpendicular to a light axis of the image-forming optical system 155.
When the sample 156 is irradiated with the optical pulse I, dye or fluorescent substances in the sample 156 are multiphoton excited, generating fluorescence. The fluorescence generated in the sample 156 transmits in the opposite direction of the incident direction of the optical pulse I, passes through the image-forming optical system 155 and the scan unit 154 and is incident on the dichroic mirror 153 to pass therethrough. Subsequently, the fluorescence having transmitted through the dichroic mirror 156 is focused onto the pinhole 158 by an image-forming optical system 157 for detection, and then incident on a detector 159 to be detected as signals. It is noted that the pinhole 158 has functions improving the resolution of the sample 156 in a light axis direction. Such a multiphoton-excited microscope system is generally referred to as a confocal laser scanning multiphoton-excited fluorescence microscope system.
Patent Document: JP 11-218490 A